The invention relates to a process for producing a first electrode and a second electrode, to an electronic component and to an electronic memory element.
For some applications in the microelectronics sector, it is desirable for the surface area of electrodes, for example of silicon electrodes or also metal electrodes, to be increased, in order, in this way, to achieve the maximum possible capacitance of the electrodes.
Enlarging the electrodes in the lateral direction is often out of the question, on account of the associated increase in space taken up by such an electrode and the resultant increase in size of an electronic component having a multiplicity of such electrodes.
For this reason, a technique for producing electrodes in which trenches are formed in a substrate has been developed, generally for electrode arrangements in three-dimensional structures in which the storage of the electrical charge carriers takes place in a stacked electrode arrangement or by using the vertically running electrodes arranged in the trenches.
However, a three-dimensional structure of this type very quickly encounters restrictions imposed by manufacturing technology, for example on account of the high aspect ratios of the trenches in which the electrodes are formed.
For this reason, it has been attempted, both when using horizontally running capacitive surfaces and vertically running capacitive surfaces, i.e. of electrodes, to increase the effective electrode surface areas while the macroscopic dimensions remain constant by roughening the respective electrode surfaces.
It is known to roughen an electrode surface, for example by means of a special etching method in order to increase the porosity of the surface or by applying additional spherical polysilicon structures to the surface of the electrodes, which are also known as hemispherical silicon grains (HSG).
During the application of spherical polysilicon structures, it is customary for polysilicon, i.e. polycrystalline silicon, to be grown onto the electrode surface which is to be roughened from a solution.
Hemispherical islands with a diameter of usually approximately 30 nm are formed on the electrode surface.
If, with a size of, for example, 30 nm, the density of these polysilicon islands is selected in such a manner that they position themselves at intervals of approximately 30 nm, it is possible to increase the surface area by well over 20%.
However, a drawback of this procedure is that the grain size of the individual hemispherical polysilicon islands which are formed cannot be controlled with accuracy and therefore an arrangement of this type can only be achieved at all with considerable process engineering problems and therefore high costs.
In the text which follows, the hemispherical islands which are formed on an electrode surface are also known as clusters.
Furthermore, [1] has disclosed a cluster ion source which is used to apply nickel clusters to a substrate surface.
In addition, it is known from [2] to form clusters from silver atoms on a graphite substrate.
Furthermore, [3] has disclosed a device for the mass separation of ion clusters, according to this particular example for the mass separation of silver clusters.
A further cluster ion source is described in [4].
[5] describes a process in which clusters of argon or phosphorus are applied to a polysilicon electrode.
Therefore, the invention is based on the problem of providing a process for producing a first electrode and a second electrode, as well as an electronic component which is formed using this method and an electronic memory element, in which it is possible for the grain size of the islands formed on the surfaces to be set more accurately.
The problem is solved by the process for producing a first electrode and a second electrode, the electronic component and the electronic memory element having the features described in the independent patent claims.
In a process for producing a first electrode and a second electrode, the first electrode and the second electrode are provided from an electrode material, which for example are integrated in a substrate, preferably in a silicon substrate.
A cluster ion source is used to apply clusters of the electrode material to the first electrode and/or second electrode.
The electrode material may be either polycrystalline silicon, i.e. polysilicon, or a metal which can in principle be selected as desired, such as nickel or silver.
The invention makes it possible, for the first time, to generate a beam profile in an accurately predeterminable manner, so that a predeterminable, if desired optimized, distribution of the clusters which are to be formed is ensured at the location of deposition, i.e. on the electrode surface of an electrode which is to be roughened.
Furthermore, the size of the clusters which are to be formed can be set very accurately.
A further advantage of the invention is that very accurate structuring of the clusters on an electrode surface is made possible in a simple and therefore inexpensive way.
According to one configuration of the invention, the electrode material may also be doped silicon, i.e. silicon clusters are formed on a silicon electrode which is doped with correspondingly desired doping atoms, the doping atoms being added to the ion beam, which is formed by the cluster ion source, comprising generated silicon ions, in a condensation area of the cluster ion source, with the result that the electrode material which is formed as clusters on the electrode surface has doped silicon clusters.
In principle, any desired electronic component which has electrodes formed in this way can be formed from the electrodes.
A preferred application area for an electrode formed in this way is electronic memories, for example an electronic memory element as a dynamic random access memory, i.e. a RAM, or a flash EEPROM.
The further development of the doping of ion beams generated in the condensation area of the cluster ion source allows very precise, simple and therefore inexpensive doping of the ion beam which was originally generated, so as to form a cluster which contains both the ions which were originally generated and the doping atoms, and therefore a cluster comprising a predeterminable number of doping atoms.
A further advantage of the invention resides in the fact that it is possible to form virtually (hemi-)spherical ion clusters, so that in this way it is potentially possible to achieve a further increase in the surface area of the electrode surface.
Furthermore, the invention makes it possible to produce cluster grain sizes which are significantly smaller than the grain sizes of the clusters which can be produced using the known method, so that even those areas of the electrode surface which adjoin relatively tight spaces may be suitable tor the area of the electrode surface to be increased.
Exemplary embodiments of the invention are illustrated in the figures and are explained in more detail below.